In a normal electronic product such as a computer, electronic devices will generate a lot of heat during operation. If the electronic devices are continuously operated at high temperature, they are easily damaged. Thus, to prevent such a damage, a heat-dissipating fan is normally disposed in the electronic product to dissipate heat to the surrounding.
Please refer to FIG. 1 which shows a conventional axial-flow fan for the computer. The conventional axial-flow fan mainly includes a housing 10, a motor 11 and an impeller 12 with a plurality of rotor blades 121. The housing 10 includes a base 14 for supporting the motor 11 and has a plurality of ribs 13 at the air outlet side of the axial-flow fan. When the motor 11 drives the impeller 12 to rotate, the blades 121 will discharge the airflow from the air outlet side of the axial-flow fan. However, according to the commonly used design, the lower edge of each rotor blade 121 is shaped in a horizontal form and the flow rate of airflow is the fastest at the end of the rotor blade. More airflow will flow in or out especially near the end edge of rotor blades. Thus, as the airflow contact the ribs 13, it will cause the mixed airflow and generate a lot of noise. It is caused by that the distance H between the lower edge of the rotor blade 121 (in a horizontal form) and the rib 13 is relatively small such that it will generate a lot of noise in a very short time as the airflow passes therethrough, thereby worsening the sound.
Thus, it is desirable to reduce the noise of the axial-flow fan generated while rotating.